1. Field of the Invention
The present invention relates to novel compositions comprising an organic semiconductor (OSC) and a wetting agent, to their use as conducting inks for the preparation of organic electronic (OE) devices, especially organic photovoltaic (OPV) cells and OLED devices, to methods for preparing OE devices using the novel formulations, and to OE devices and OPV cells prepared from such methods and compositions.
2. Background and Prior Art
When preparing OE devices like OFETs or OPV cells, in particular flexible devices, usually printing or coating techniques like inkjet printing, roll to roll printing, slot dye coating or flexographic/gravure printing are used to apply the OSC layer. Based on low solubility of the most of the present organic compounds useful as OSC these techniques need the use of solvents in high amounts. In order to reduce solvent de-wetting and to increase dry film levelness surfactants can be used. These additives are especially needed with regard to small molecular OSC or polymeric OSC having a low molecular weight. The use of conventional surfactants or wetting agents is disclosed, e.g. in WO 2009/049744. However, no explicit examples are mentioned. Based on the low solubility of the most of the OSC materials the amounts of surfactants needed are high in relation to the amount of OSC material in an ink formulation.
U.S. Pat. No. 5,326,672 discloses the use of volatile surfactants to control the rinsing of a resist structure in order to give improved line definition. However, the composition comprising the volatile surfactants is not used to apply any components to a surface but to rinse the developed resist pattern. No composition is disclosed comprising any OSC material.
Furthermore, volatile surfactants for cleaning electric and electronic parts are disclosed in EP 1 760 140 B1. However, EP 1 760 140 B1 does not provide any hints to use these wetting agents in a composition for applying any layer on a surface.
JP 2003-128941 A discusses the formulation of a photo-curing formulation which gives enhanced resistance properties. According to the teaching of JP 2003-128941A a water emulsion for applying a photoresist layer can be used in order to provide environmental improvements. No composition is disclosed comprising any OSC material.
JP 5171117 A relates to the addition of a volatile surfactant to a tacky acrylic resin and a reactive surfactant to form an emulsion. The composition is used for forming a tape in wafer processing. No composition is disclosed comprising any OSC material.
In prior art volatile surfactants or wetting agents are used to improve the adhesion of a layer formed before applying a composition comprising the wetting agent or of a layer being applied after a rinsing step. However, in the field of OSC materials, the adhesion of the layers formed with conventional surfactants is not critical. Furthermore, the OE devices as disclosed in WO 2009/049744 show useful efficiencies and lifetimes. However, it is a permanent desire to improve the performance of the OSC layer, such as efficiency, lifetime and sensitivity regarding oxidation or water.
It is therefore desirable to have fluids comprising an OSC that are suitable for the preparation of OE devices, especially thin film transistors, diodes, OLED displays and OPV cells, which allow the manufacture of high efficient OE devices having a high performance, a long lifetime and a low sensitivity against water or oxidation. One aim of the present invention is to provide such improved fluids. Another aim is to provide improved methods of preparing an OE device from such fluids. Another aim is to provide improved OE devices obtained from such fluids and methods. Further aims are immediately evident to the person skilled in the art from the following description.
Surprisingly it has been found that these aims can be achieved, and the above-mentioned problems can be solved, by providing methods, materials and devices as claimed in the present invention, especially by providing a process for preparing an OE device using a composition comprising a volatile wetting agent.